Reflector formed with highly reliable conductive pattern, process for fabricating reflector and liquid crystal display unit using the same

ABSTRACT

A reflector is incorporated in a liquid crystal display panel for directing light to an optical path from a lamp to a liquid crystal panel, and a high voltage line is directly connected to an electrode of the lamp, but a low voltage line is connected through a conductive pattern formed on the reflector to the other electrode of the lamp, wherein the conductive pattern is formed from a layer of conductive filler printed on the reflector through thermosetting so that the conductive pattern is thick enough to withstand thermal stress without enlargement of the liquid crystal display unit.

FIELD OF THE INVENTION

This invention relates to a liquid crystal display unit and, moreparticularly, to a liquid crystal display unit with a reflector, thereflector and a process for producing the reflector.

DESCRIPTION OF THE RELATED ART

The liquid crystal display unit is broken down into a liquid crystalpanel, a driving circuit and a light source. Liquid crystal is sealed inthe liquid crystal panel, and the driving circuit makes the liquidcrystal panel partially vary the transparency of the liquid crystal.Light is radiated from the light source through the liquid crystalpanel, and the transmitted light produces images on the liquid crystalpanel. Thus, the light source is an important element of the liquidcrystal display unit.

The light source includes a lamp, an optical guide plate, a reflectorand a power supply cable. The optical guide plate is registry with theliquid crystal panel, and the lamp is opposed to a side surface of theoptical guide plate. The lamp is encircled with the reflector. When theelectric power is supplied through the power supply cable to the lamp,the light is radiated from the lamp. The light is partially incidentonto the side surface of the optical guide plate. Most of the remaininglight is radiated toward the reflector, and is reflected from thereflector toward the optical guide plate. The incident light ispropagated through the optical guide, and the liquid crystal panel,i.e., the array of pixels is uniformly illuminated by the optical guideplate.

FIG. 1 shows a typical example of the prior art liquid crystal unit. Theprior art liquid crystal display unit largely comprises a light source1, a liquid crystal panel 5 and a circuit board 6. The driving circuitis integrated on the circuit board 6, and the circuit board 6 isattached to a side surface of the liquid crystal panel 5. The lightsource 1 is assembled with the liquid crystal panel 5, and the liquidcrystal panel 5, the light source 1 and the circuit board 6 areaccommodated in a suitable housing (not shown).

The light source 1 includes a reflector 2, a power supply cable 3, anoptical guide plate 4 and a lamp 10. The optical guide plate 4 is aswide as the liquid crystal panel 5, and has a light output surface. Thelight output surface is opposed to the back surface of the liquidcrystal panel, and the reflector is attached to the side portion of theoptical guide plate 4. The reflector has a reflecting surface, whichdefines a space together with the side surface of the optical guideplate 4. The lamp 10 has a column shape, and is provided in the space.The power supply cable 3 is connected to the lamp 10, and electric poweris supplied through the power supply cable 3 to the lamp 10.

The lamp 10 has the column shape, and electrodes are formed on both endsurfaces of the lamp 10. The reflector 2 is as long as the lamp 10 (seeFIG. 2), and has a channel shape. The upper/lower plate portions projectfrom the upper/lower ends of the vertical plate portion 2 a. The lamp 10is located between the upper plate portion and the lower plate portion,and the electrodes are exposed to both ends of the space definedtherebetween. The power supply cable has a high voltage line 3 a, a lowvoltage line 3 b and a round cable 32. Though not shown in FIGS. 1 to 3,the high voltage line 3 a and the low voltage line 3 b are connected toan electric power source. The high voltage line 3 a is directlyconnected to the electrode, and the low voltage line 3 b is connectedthrough the round cable 32 to the other electrode. The round cable 32 isas long as the reflector 2, and is provided on the vertical plateportion 2 a. The round cable 32 has a circular cross section, and thediameter ranges from 0.5 millimeter to 1.0 millimeter as shown in FIG.3.

A problem is encountered in that wide space is occupied by the prior artlight source. This is because of the fact that the round cable used forconnecting the low voltage line 3 b to the electrode of the lamp 10. Theround cable per se occupies the wide space, and requires additionalspace between the round cable and another component part.

A flexible flat cable was proposed. FIGS. 4 and 5 show another prior artlight source 1. The prior art light source also includes a reflector, alamp and a power supply cable 32. The reflector and the lamp are similarto those of the prior art light source shown in FIGS. 1 to 3, and arelabeled with the same references. The power supply cable 32 includes thehigh voltage line 3 a, the low voltage line 3 b and a flexible flatcable 33. The high voltage line 3 a and the low voltage line are alsoconnected to an electric power source (not shown). The high voltage line3 a is directly connected to the electrode of the lamp 10, and the lowvoltage line 3 b is connected through the flexible flat cable 33 to theother electrode of the lamp 10. The flexible flat cable 33 is fixed tothe vertical portion 2 a of the reflector 2 by means of adhesivecompound 34. The flexible flat cable 33 is 0.2 millimeter thick, and theadhesive compound layer 34 is of the order of 0.1 millimeter thick. Thetotal thickness is of the order of 0.3 millimeter. Thus, the spaceoccupied by the interconnecting cable is reduced by virtue of theflexible flat cable 33.

Research and development efforts are being made on a compact liquidcrystal display panel with wide image production area. This technicalgoal is to be achieved by reducing the frame area, i.e., the peripheralarea around the image production area. The interconnecting cables 32/33are positioned under the frame area, and, accordingly, havenon-ignoreable influence on the frame area. Although the usage of theflexible flat cable 33 results in a fairly narrow frame area, the totalthickness of 0.3 millimeter is too far from the goal.

A thin interconnection is proposed in Japanese Patent Publication ofUnexamined Application No. 10-206847. FIG. 6 shows the prior art liquidcrystal display unit disclosed therein. The circuit board 6 is providedon one side portion of the liquid crystal display panel 5, and theoptical guide plate 4 is overlapped with the liquid crystal displaypanel 5 and the circuit board 6. A light source 35 is provided on oneside of the optical guide plate 4, and also includes a reflector 2, alamp 10 and a power supply cable 35. A space is defined by the reflector2 and the optical guide plate 4, and the lamp 10 is provided in thespace. Electric power is supplied from an electric power source throughthe power supply cable to the lamp 10. The high voltage line (notshown), the low voltage line (not shown) and an interconnection 36 formthe power supply cable 35. The interconnection 36 is implemented by athin conductive layer deposited on the outer surface of the reflectorthrough an evaporation technique. The interconnection 36 ranges from0.0005 millimeter thick to 0.001 millimeter thick. The interconnection36 is drastically reduced in thickness, and makes the frame area narrow.

The interconnection 36 is conducive to the reduction of the frame area.However, the interconnection 36 deposited through the evaporationtechnique is less reliable. Disconnection, cracks and peel-off areliable to take place after the completion of the liquid crystal displaypanel. The disconnection, cracks and peel-off are due to thermal stressor other external force exerted on the extremely thin interconnection.Not only the light but also heat is radiated from the lamp 10, and theheat raises the temperature of the reflector 2. The difference inthermal expansion coefficient between the reflector and theinterconnection 36 gives rise to the thermal stress, and the extremelythin interconnection can not withstand the thermal stress. Whenmechanical force is undesirably exerted on the reflector 2, thereflector 2 is deformed, and the extremely thin interconnection can notwithstand the deformation.

Another problem inherent in the prior art interconnection 36 is highproduction cost. The evaporation system is expensive, and the throughputis not large. The extremely thin interconnection is deposited throughthe expensive evaporation system at a low throughput. This results inthe high production cost.

SUMMARY OF THE INVENTION

It is therefore an important object of the present invention to providea reflector on which a durable thin interconnection is formed.

It is also an important object of the present invention to provide aprocess for economically producing the reflector.

It is another important object of the present invention to provide aliquid crystal display unit equipped with the reflector.

To accomplish the object, the present invention proposes to solidify alayer of conductive filler printed on a reflector for producing aconductive pattern.

In accordance with one aspect of the present invention, there isprovided a reflector comprising a body formed of insulating resin andhaving an outer surface and an inner surface defining a space open to anobject to which a light is to be directed, and a conductive patternprinted on the outer surface for supplying an electric power to a lightsource placed in the space.

In accordance with another aspect of the present invention, there isprovided a liquid crystal display unit for producing an image comprisinga liquid crystal panel having an incident surface and an image producingsurface, a driving circuit connected to the liquid crystal panel andvarying the transparency of a part of the liquid crystal panel so as totransmit a light from the incident surface to the image producingsurface through the part, and a light source illuminating the lightincident surface with the light and including a lamp having electrodesand generating the light propagated along an optical path to the liquidcrystal panel, a power supply cable having a conductive pattern andvoltage application lines directly connected to one of the electrodesand connected through the conductive pattern to the other of theelectrodes and a reflector formed of an insulating resin and having anouter surface where the conductive pattern is printed and an innersurface defining a space accommodating the lamp and open to the opticalpath for directing the light to the optical path.

In accordance with yet another aspect of the present invention, there isprovided a process for producing a reflector comprising the steps of a)forming an insulating member from a first synthetic resin, b) printing aconductive filler on a surface of the insulating member, and c)solidifying the conductive filler on the surface for producing aconductive pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the reflector, the process and the liquidcrystal display unit equipped with the reflector will be more clearlyunderstood from the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a perspective view showing the structure of the prior artliquid crystal display unit;

FIG. 2 is a perspective view showing the component parts of the priorart light source;

FIG. 3 is a cross sectional view taken along line B-B of FIG. 2 andshowing the structure of the prior art light source;

FIG. 4 is a perspective view showing the component parts of the priorart light source;

FIG. 5 is a cross sectional view taken along line C-C of FIG. 4 andshowing the structure of the prior art light source;

FIG. 6 is a schematic cross sectional view showing the structure of theprior art liquid crystal display unit disclosed in Japanese PatentPublication of Unexamined Application No. 10-206847;

FIG. 7 is a perspective view showing the structure of a light sourceaccording to the present invention in disassembled state;

FIG. 8 is a cross sectional view taken along line A-A of FIG. 7 andshowing the structure of the light source;

FIG. 9 is a schematic cross sectional view showing the structure of aliquid crystal display unit according to the present invention;

FIG. 10 is a schematic view showing the structure of an extrusionmolding machine used in a process according to the present invention;

FIG. 11 is a schematic view showing the structure of the extrusionmolding machine used in another process according to the presentinvention;

FIG. 12 is a cross sectional view showing another reflector according tothe present invention; and

FIG. 13 is a perspective view showing the structure of yet anotherreflector according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Reflector

Referring to FIGS. 7 and 8 of the drawings, a light source 1 embodyingthe present invention comprises a reflector 2, a light source 10, apower supply cable 38 and an optical guide plate 4 (see FIG. 9). Thelamp 10 is placed in an inner space defined in the reflector 2, andelectric power is supplied from an electric power source (not shown)through the power supply cable 38 to the lamp 10. When the lamp 10 isenergized, light is radiated from the lamp 10, and part of the light isreflected on the inner surface of the reflector 2 so as to be directedtoward the optical guide plate 4.

The reflector 2 has a channel shape, and is broken down into a verticalplate portion 2 a, a relatively short upper plate portion projectingfrom the upper edge of the vertical plate portion 2 a and a relativelylong lower plate portion projecting from the lower edge of the verticalplate portion 2 a. The inner space is defined between the relativelyshort upper plate portion and the relatively long lower plate portion.The reflector 2 is formed of thermoplastic resin such as, for example,polyethylene terephthalate resin. Polycarbonate resin may be used forthe reflector 2. These kinds of resin are insulating material, and donot ally electric current to flow therethrough.

A conductive pattern 31 is formed on the vertical plate portion 2 a. Theconductive pattern 31 straightly extends from one end of the reflector 2to the other end. In other words, the conductive pattern 31 is formedalong the shortest path in a longitudinal direction of the reflector 2.As described hereinbefore, the reflector 2 is formed of the insulatingmaterial, and, accordingly, any leakage current flows from theconductive pattern 31 through the reflector 2. The conductive pattern 31may be screen printed on the vertical plate portion 2 a of the reflector2.

The conductive pattern 31 is formed of thermosetting resin, and is ofthe order of 0.03 millimeter thick. The thermosetting resin is flexible,and the cracks are less liable to take place in the conductive pattern31 by virtue of the large flexibility. Moreover, the conductive pattern31 is fairly thick. Although the conductive pattern 31 is thicker thanthe prior art conductive pattern 36 between 0.0005 millimeter thick to0.001 millimeter thick, the conductive pattern 31 is thinner than theround cable 10 ranging between 0.5 millimeter thick and 1.0 millimeterthick and the flexible flat cable/adhesive compound layer 33/34 of 0.2millimeter thick plus 0.1 millimeter thick. The large thickness rendersthe conductive pattern 31 withstanding the thermal stress, and thedisconnection is less liable to take place.

The thermosetting resin is formed from a layer of conductive filler,which is screen printed on the vertical plate portion 2 a. Theconductive filler may be modified copolymerized polyester mixed withsilver (Ag) and carbon (C). The thermosetting resin is large in adhesionto the polyethylane terephthalate resin, and the flexibility is large.For this reason, even though the thermal stress is exerted on thereflector 2, the conductive pattern 31 hardly peels off from thereflector 2.

The lamp 10 has a column shape, and a pair of electrodes 11/12 is formedon the end surfaces of the lamp 10. The electrode 11 is formed on oneend surface of the lamp 10, and high voltage is applied to the electrode11. The other electrode 12 is formed on the other end surface of thelamp 10, and low voltage is applied through the conductive pattern 31 tothe electrode 12. The lamp 10 is supported by the reflector 2 by meansof a suitable retainer (not shown).

Liquid Crystal Display Unit

Turning to FIG. 9 of the drawings, the light source 1 is incorporated ina liquid crystal display unit. The liquid crystal display unit furthercomprises a liquid crystal panel 5 and a circuit board 6. A drivingcircuit is integrated on the circuit board 6. The circuit board 6 isprovided along a side line of the liquid crystal panel 5, and isconnected to the liquid crystal panel 5. The optical guide plate 4 isoverlapped with the liquid crystal panel 5 and the circuit board 6.Thus, the liquid crystal panel 5, the circuit board 6 and the lightsource 1 are assembled together, and are accommodated in a case 40.

When the lamp 10 is energized, light is radiated from the lamp 10 to theoptical guide plate 4, and part of the light is reflected on the innersurface of the reflector 2. The reflected light is also incident ontothe side surface of the optical guide plate 4. The light is propagatedthrough the optical guide plate 4, and is output from the upper surfaceof the optical guide plate 4. Thus, the liquid crystal panel 5 isilluminated with the light. The driving circuit supplies animage-carrying signal and the scanning signal to data electrodes andscanning electrodes of the liquid crystal panel 5, and the transparencyof the liquid crystal is partially changed. As a result, the lightpasses the transparent portions of the liquid crystal panel 5, and animage is produced on the liquid crystal panel 5.

While the driving circuit is producing the image on the liquid crystalpanel 5, not only light but also heat is radiated toward the reflector2, and the heat raises the temperature of the reflector 2. The heat iscausative of the thermal stress. However, the conductive pattern 31 isthick enough to withstand the thermal stress. For this reason, thedisconnection and the cracks are less liable to take place in theconductive pattern 31.

The image is produced on an image producing area of the liquid crystalpanel 5. The liquid crystal panel 5 is exposed to a central area of thecase 40. However, the peripheral area of the case is not available forthe image production. As described hereinbefore, the low voltage isapplied through the conductive pattern 31 to the electrode 12 of thelamp 10, and the conductive pattern 31 is of the order of 0.03millimeter thick. This means that the manufacturer designs the case 40in such a manner as to make the side plate 40 a close to the reflector2. The case 40 is compact. However, the image producing area is notreduced. Thus, the light source 1 according to the present invention isconducive to the compact liquid crystal display unit without sacrificeof the image production area.

Process

Description is firstly made on a process for producing the reflector 2.A manufacturing machine is used in the process. The manufacturing systemis broken down into an extrusion molding machine 40, a printing machine50, a cutting machine 55 and a thermosetting unit (not shown). Theextrusion molding machine 40 produces a channel bar 59 from rawmaterial, and the conductive pattern 31 is formed on the channel bar 59by means of the printing machine 50. The channel bar 59 is cut intoplural short channel bar 2 a by means of the cutting machine 55, and thereflector 2 are obtained through the thermosetting unit (not shown).

The extrusion molding machine 40 includes a heating cylinder 41, ahopper 42, a screw (not shown), an electric motor 43, a die nozzle 44, aforming die 45 and a cooling vessel 46. The hopper 42 is attached to theheating cylinder 41, and the row material is supplied through the hopper42 into the inner space of the heating cylinder 41. The raw material isheated so as to be softened. The screw (not shown) is provided in theinner space, and is driven for rotation by means of the electric motor43. The soft material is pushed out through the die nozzle 44, and a bar60 is pushed out. The bar 60 is shaped into the channel bar 59 by meansof the forming die 45, and is cooled in the cooling vessel 46 forsolidifying the channel bar 59. Thus, the channel bar 59 is output fromthe cooling vessel 46.

The printing machine 50 includes a dispenser 51. The conductive filleris supplied through a tube 52 to the dispenser 51, and the conductivefiller 31 a is printed on the vertical plate portion of the channel bar59. The cutting machine 55 includes a driving roller 56 and a cuttingblade 57. The driving roller 56 moves the channel bar 59 toward thecutting machine 55, and the channel bar 59 is cut into plural shortchannel bars 2 a by means of the cutting blade 57. The short channelbars 2 a are conveyed to the thermosetting unit (not shown), and theprinted layers of conductive filler 31 a are cured in the thermosettingunit (not shown). Thus, the reflector 2 with the conductive pattern 31is continuously manufactured.

In the process described hereinbefore, the conductive filler is printedon the vertical plate portion of the channel bar 59 after the coolingstep. However, the conductive filler may be printed on the verticalplate portion of the bar 60 before the cooling step as shown in FIG. 11.The bar 59 is hot. When the conductive filler is printed on the hot bar60, the conductive filler is partially solidified through the heatexchange between the hot bar 60 and the conductive filler. This resultsin enhancement of adhesion between the reflector 2 and the conductivepattern 31.

As will be appreciated from the foregoing description, the conductivefiller is printed on the reflector 2, and the layer of conductive filleris thermally cured. The printing technique is suitable to give theappropriate thickness to the conductive pattern 31. Thus, the reflector2 with the conductive pattern 31 is produced through the processdescribed hereinbefore. The printing technique does not require a longtime, and is rather economical than the evaporation. The throughput isimproved, and the production cost is surely reduced.

Moreover, the channel bar 59 with the layer of conductive filler iscontinuously produced through the manufacturing system at high speed.The throughput is further improved, and the production cost isdrastically reduced.

Finally, the conductive filler is printed by using the dispenser 51. Thedispenser 51 shapes the conductive filler in a stripe on the channel bar59. For this reason, any mask is required for the printing stage.

Second Embodiment

Turning to FIG. 12 of the drawings, another reflector 2 c embodying thepresent invention is formed with a groove elongated in the longitudinaldirection thereof. The groove is formed in the vertical plate portion 2a of the reflector 2 c, and is of the order of 0.03 millimeter deep. Theconductive filler is printed on the bottom surface of the groove, and issolidified through the thermosetting. The conductive pattern 31 isperfectly embedded in the vertical portion of the reflector 2 c, and iscoplanar with the surface of the vertical plate portion 2 a. Using thereflector 2 c, the liquid crystal display unit is further made compact.The groove may be formed in the channel bar through a forming die.

As will be appreciated from the foregoing description, the conductivepattern 31 is printed on the reflector 2, and the printing techniquegives an appropriate thickness to the conductive pattern 31. Althoughthe thermal stress is exerted on the conductive pattern 31, the thickconductive pattern 31 withstands the thermal stress, and is free fromthe disconnection and cracks.

The reflector 2 and the conductive pattern 31 are respectively formed ofconductive thermosetting resin and insulating thermoplastic resin, andthe conductive thermosetting resin exhibits good adhesion to theinsulating thermoplastic resin. Moreover, the conductive thermosettingresin is flexible. For this reason, the conductive pattern 31 is hardlyseparated from the reflector 2. Thus, the conductive pattern 31 is freefrom the peel-off.

The conductive pattern 31 is expected to achieve large resistanceagainst the thermal stress as well as the narrow occupation space. Fromthis aspect, the thickness of the conductive pattern is fallen within acertain range. The good adhesion between the thin conductive pattern 31and the reflector 2 is resulted from the thermosetting resin and thethermoplastic resin in the above-described embodiments. The othercombinations of the materials are available for them.

Although particular embodiments of the present invention have been shownand described, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the present invention.

A multiple conductive pattern 31 b, i.e., plural conductive stripes maybe formed on the vertical plate portion 2 a in parallel to one anotheras shown in FIG. 13. In this instance, even if disconnection takes placein one of the plural conductive stripes, the other conductive stripespropagate the low voltage from the low voltage line 3 b to the electrode12. Thus, the multiple conductive pattern enhances the reliability ofthe interconnection 31.

The conductive filler may be printed on the vertical plate portion 2 athrough a mask by using a squeegee as popular in the screen printing.

A reflector according to the present invention may be used in anotheroptical device such as a lighting device.

1-15. (canceled)
 16. A process for producing a reflector, comprising:forming an insulating member from a first synthetic resin; printing aconductive filler on a surface of said insulating member; andsolidifying said conductive filler on said surface for producing aconductive pattern.
 17. The process as set forth in claim 16, in whichsaid first synthetic resin comprises a thermoplastic resin, and saidconductive pattern comprises a second synthetic resin implementing athermosetting resin containing a conductive material.
 18. The process asset forth in claim 17, in which said thermoplastic resin is selectedfrom the group consisting of polyethylene terephthalate resin andpolycarbonate resin, and said conductive filler contains modifiedcopolymerized polyester, silver and carbon.
 19. The process as set forthin claim 16, in which said forming includes: heating said firstinsulating resin for producing a soft insulating resin, extruding saidsoft insulating resin for forming a hot bar member, and cooling said hotbar member for producing said insulating member.
 20. The process as setforth in claim 16, in which said forming includes: heating said firstinsulating resin for producing a soft insulating resin, and extrudingsaid soft insulating resin for forming a hot bar member serving as saidinsulating member.
 21. The process as set forth in claim 16, in whichsaid conductive filler is printed by using a dispenser.